Directional backlight unit, three-dimensional (3d) image display apparatus, and 3d image displaying method

ABSTRACT

A directional backlight unit, a three-dimensional (3D) image display apparatus, and a 3D image displaying method are provided. The directional backlight unit includes a light guide plate having an emission surface on which a plurality of grating elements including first and second groups of grating elements are provided. The plurality of grating elements are arranged such that light beams emitted from the first and second groups of grating elements commonly propagate through a plurality of pixel points and respectively form first and second groups of view points of which corresponding regions do not overlap with each other.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims priority from Korean Patent Application No.10-2016-0008910, filed on Jan. 25, 2016, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference in its entirety.

BACKGROUND

1. Field

Exemplary embodiments relate to directional backlight units,three-dimensional (3D) image display apparatuses, and 3D imagedisplaying methods, and more particularly, to a grating-baseddirectional backlight unit, a 3D image display apparatus, and a 3D imagedisplaying method.

2. Description of the Related Art

Three-dimensional (3D) image display apparatuses enable users toexperience realistic and stereoscopic images. In general, 3D imagedisplay apparatuses provide a 3D effect by using a binocular parallaxthat appears when images at different view points are seen by the leftand right eyes. In the conventional art, glasses-type 3D imagedisplaying methods using red-green glasses, polarizing glasses, liquidcrystal shutter type glasses, or the like were primarily developed. Inrecent years, autostereoscopic 3D image displaying methods removing theinconvenience of using glasses have been actively studied. Examples ofautostereoscopic 3D image displaying methods include a method ofdisplaying several images having different view points according todirections by using a lenticular lens, a parallax barrier, or the like;integrated image technology, which is a method of capturing images atseveral angles by using a plurality of cameras or lenses and displayingthe images inversely; and a holography method. Among theseautostereoscopic 3D image realizing technologies, a technology relatedwith a method of constructing a 3D image by respectively transmittinglight beams from pixels in desired directions by using a recentdirectional backlight unit is being developed.

SUMMARY

Provided are directional backlight units that provide a wide watchingangle, three-dimensional (3D) image display apparatuses, and 3D imagedisplaying methods.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented exemplary embodiments.

According to an aspect of one or more exemplary embodiments, adirectional backlight unit includes a light guide plate; a light sourceconfigured to provide light to the light guide plate; and first andsecond groups of grating elements disposed on an emission surface of thelight guide plate and configured to externally emit the light from theemission surface, wherein the first and second groups of gratingelements are arranged such that light beams emitted from the first groupof grating elements propagate through a plurality of pixel points spacedapart from the emission surface and form a first group of view points,that light beams emitted from the second group of grating elementspropagate through the plurality of pixel points and form a second groupof view points, and that a region within which the second group of viewpoints are formed does not overlap with a region within which the firstgroup of view points are formed. The plurality of pixel points indicatepoints where pixels of a spatial light modulator which will be describedbelow are located. The plurality of pixel points may betwo-dimensionally arranged on a plane or a curved surface.

The view points in the first group may be consecutively arranged, andthe view points in second group may be consecutively arranged after thefirst group of view points.

A third group of grating elements may be further disposed on the lightguide plate. In this case, the third group of grating elements isarranged such that light beams emitted from the third group of gratingelements propagate through the plurality of pixel points and form athird group of view points and that a region within which the thirdgroup of view points is formed does not overlap with a region withinwhich the first and second groups of view points are formed. Forexample, the view points in the third group of view points may beconsecutively arranged after the second group of view points.

At least two light beams may propagate through each of the plurality ofpixel points, and the at least two light beams may include a light beamemitted from one of the grating elements included in the first group anda light beam emitted from one of the grating elements included in thesecond group.

According to an exemplary embodiment, light beams emitted from twoadjacent grating elements among the first and second groups of gratingelements may be directed to different pixel points. According to anotherexemplary embodiment, some of the light beams emitted from two adjacentgrating elements among the first and second groups of grating elementsmay be directed to the same pixel point.

The first and second groups of grating elements may include a pluralityof patterned grooves that are substantially parallel to one another. Thefirst and second groups of grating elements may be different from eachother with respect to at least one of a grating length, a grating width,a grating depth, a grating orientation, a grating pitch, and a dutycycle. For example, the grating elements may have different gratingorientations or different grating pitches so that light beams emittedfrom the grating elements may have different directions.

At least some of the first and second groups of grating elements may bedifferent from each other in an arrangement interval.

Intervals between the first and second groups of grating elements andthe plurality of pixel points may be substantially constant. A virtualpixel surface on which the pixel points are located, or the emissionsurface of the light guide plate may be a curved surface. If the virtualpixel surface on which the pixel points are located is a plane, theemission surface of the light guide plate is also a plane, and thevirtual pixel surface on which the pixel points are located may beparallel to the emission surface of the light guide plate.

The number of grating elements in the first group may be substantiallythe same as the number of pixel points. In other words, the gratingelements in the first group may match with the pixel points in aone-to-one correspondence.

The number of grating elements in the first group may be substantiallythe same as the number of grating elements in the second group. In thiscase, the number of view points in the second group formed by the secondgroup of grating elements may be equal to the number of view points inthe first group formed by the first group of grating elements. In somecases, the number of grating elements in the second group may be lessthan or more than the number of grating elements in the first group.When the number of grating elements in the second group is less than thenumber of grating elements in the first group, a resolution at thesecond group of view points formed by the second group of gratingelements may be lower than a resolution at the first group of viewpoints formed by the first group of grating elements.

The light guide plate may include a single light guide plate. In thiscase, the first and second groups of grating elements may form a singlegrating array on the emission surface of the light guide plate. Thelight guide plate may be a flat panel having a flat emission surface ora plate having a curved emission surface. The emission surface of thelight guide plate and the surface on which the plurality of pixel pointsare located may be apart by a predetermined distance from each other. Asanother example, one of the emission surface of the light guide plateand the surface on which the plurality of pixel points are located maybe a curved surface, and the other may be a plane, and thus an intervalbetween the light guide plate and the spatial light modulator may bevariable.

The light guide plate may include a first light guide plate and a secondlight guide plate that are optically separated from each other, some ofthe grating elements in the first and second groups may be disposed onthe first light guide plate, and the others may be disposed on thesecond light guide plate.

The number of grating elements provided on each of the first and secondlight guide plates may be substantially the same as the number of pixelpoints. In some cases, the number of grating elements provided on thefirst light guide plate may be less than or more than the number ofgrating elements provided on the second light guide plate. The firstgroup of grating elements may be provided on the first light guide plateand the second group of grating elements may be provided on the secondlight guide plate.

The first and second light guide plates may be disposed side by side ina lateral direction. The lateral direction denotes a direction toward aleft side, a right side, a top side, or a bottom side of a plate. Inother words, the first and second light guide plates may be arrangedtwo-dimensionally. The first and second light guide plates may be flatpanels having flat emission surfaces or curved emission surfaces. Thesecond light guide plate may be inclined with respect to the first lightguide plate. Of course, the first and second light guide plates may bearranged on a plane.

A third light guide plate may be further included, and thus the secondand third light guide plates may be stacked one on another or arrangedside by side, with the first light guide plate therebetween. The secondand third light guide plates may be inclined with respect to the firstlight guide plate so that the second and third light guide plates aresymmetrical about the first light guide plate. Of course, the firstthrough third light guide plates may be arranged on a plane.

The first light guide plate may be stacked over an upper surface of thesecond light guide plate. The upper surface of the second light guideplate may denote an emission surface of the second light guide plate.The first and second light guide plates may be stacked without spacestherebetween or with a slight space therebetween. Since the third lightguide plate is further included, the first through third light guideplates may be stacked one on another.

According to an aspect of one or more exemplary embodiments, adirectional backlight unit includes a light guide plate; a light sourceconfigured to provide light to the light guide plate; and k groups ofgrating elements disposed on an emission surface of the light guideplate and configured to externally emit the light from the emissionsurface, wherein the k groups of grating elements are arranged such thatlight beams emitted from an l-th group of grating elements pass througha plurality of pixel points spaced apart from the emission surface andform an l-th group of view points, that light beams emitted from an m-thgroup of grating elements pass through the plurality of pixel points andform an m-th group of view points, and that a region where the m-thgroup of view points is formed does not overlap with a region where thefirst group of view points is formed, and wherein k may be a naturalnumber, l may be a natural number smaller than or equal to k, and m maybe a natural number smaller than l.

According to an aspect of one or more exemplary embodiments, adirectional backlight unit includes a light guide plate; a light sourceconfigured to provide light to the light guide plate; and a plurality ofgrating elements disposed on an emission surface of the light guideplate and configured to externally emit the light from the emissionsurface such that the light propagates through a plurality of pixelpoints spaced apart from the emission surface, wherein at least two ofthe plurality of grating elements match with each pixel point, twoadjacent grating elements match with different pixel points, and lightbeams emitted from the at least two grating elements pass through onepixel point matched with the at least two grating elements and then aredirected toward different view points. The overall number of gratingelements may be an integer multiple of the number of pixel points. Theplurality of grating elements may be arranged such that light beamsemitted from the plurality of grating elements pass through theplurality of pixel points and form a plurality of groups of view pointsand that regions where different groups of view points are formed do notoverlap with each other.

According to an aspect of one or more exemplary embodiments, athree-dimensional (3D) image display apparatus includes a directionalbacklight unit comprising a light guide plate, a light source configuredto provide light to the light guide plate, and first and second groupsof grating elements disposed on an emission surface of the light guideplate and configured to externally emit the light from the emissionsurface; a spatial light modulator comprising a plurality of pixels thatmodulate light beams emitted from the directional backlight unit; and acontroller configured to control the directional backlight unit and thespatial light modulator, wherein the first and second groups of gratingelements are arranged such that light beams emitted from the first groupof grating elements pass through the plurality of pixels of the spatiallight modulator and form a first group of view points, that light beamsemitted from the second group of grating elements pass through theplurality of pixels of the spatial light modulator and form a secondgroup of view points, and that a region where the second group of viewpoints are formed does not overlap with a region where the first groupof view points are formed. The spatial light modulator may include aplurality of pixels that are two-dimensionally arranged. The spatiallight modulator may be a flat panel or a curved plate. In other words,the pixels of the spatial light modulator may be located on a flat panelor a curved plate.

The view points in the first group may be consecutively arranged, andthe view points in second group may be consecutively arranged after thefirst group of view points.

At least two light beams may pass through each of the plurality of pixelpoints, and the at least two light beams may include a light beamemitted from one of the grating elements included in the first group anda light beam emitted from one of the grating elements included in thesecond group.

3D images shown at the first group of view points may be repeatedlyshown at the second group of view points.

The spatial light modulator may include a plurality of sub-pixels foreach pixel, and each of the sub-pixels of the spatial light modulatormay transmit light beams emitted from at least two grating elements.

Each of the sub-pixels may have a rectangular shape that is longer inone direction or a shape similar to the rectangular shape. The pluralityof sub-pixels in each pixel may be arranged side by side in a widthdirection thereof. In a lengthwise direction of the sub-pixels, theoverall number of rows of the first and second groups of gratingelements may be an integer multiple of the number of rows of thesub-pixels.

The 3D image display apparatus may further include an eye trackingdevice configured to track eyes of a viewer. The controller may controlthe spatial light modulator so that pixels corresponding to the eyes ofthe viewer tracked by the eye tracking device generate an image. If theviewer moves from the first group of view points to the second group ofview points or moves from the second group of view points to the firstgroup of view points, a reversal between the left and right sidesoccurs, and a stereoscopic effect may be destroyed. Occurrence of thereversal between the left and right sides may be prevented by moving theview points in advance.

According to an aspect of one or more exemplary embodiments, athree-dimensional (3D) image display apparatus includes a directionalbacklight unit; a spatial light modulator including a plurality ofpixels that modulate light beams emitted from the directional backlightunit; and a controller configured to control the directional backlightunit and the spatial light modulator. The directional backlight unit mayinclude a light guide plate, a light source configured to provide lightto the light guide plate, and a plurality of grating elements disposedon an emission surface of the light guide plate and configured toexternally emit the light from the emission surface such that the lightpropagates through the plurality of pixels of the spatial lightmodulator. At least two of the plurality of grating elements match witheach pixel, two adjacent grating elements match with different pixels,and light beams emitted from the at least two grating elements passthrough one pixel matched with the at least two grating elements andthen are directed toward different view points.

According to an aspect of one or more exemplary embodiments, a 3D imagedisplaying method includes providing light to a light guide plate;arranging a plurality of grating elements comprising first and secondgroups of grating elements on an emission surface of the light guideplate to externally emit the light from the emission surface; modulatingemitted light beams by using a plurality of pixels of a spatial lightmodulator; and forming a first group of view points by allowing lightbeams emitted from the first group of grating elements to pass throughthe plurality of pixels of the spatial light modulator and forming asecond group of view points by allowing light beams emitted from thesecond group of grating elements to pass through the plurality of pixelsof the spatial light modulator, wherein a region within which the secondgroup of view points is formed does not overlap with a region withinwhich the first group of view points is formed.

The view points in the first group may be consecutively arranged, andthe view points in the second group may be consecutively arranged afterthe first group of view points.

At least two light beams may pass through each of the plurality of pixelpoints, and the at least two light beams may include a light beamemitted from one of the grating elements included in the first group anda light beam emitted from one of the grating elements included in thesecond group.

Light beams emitted from two adjacent grating elements among the firstand second groups of grating elements may be directed to differentpixels.

3D images shown at the first group of view points may be repeatedlyshown at the second group of view points.

The 3D image displaying method may further include tracking eyes of aviewer. The spatial light modulator may be controlled so that pixelscorresponding to the tracked eyes of the viewer generate an image.

In the provided directional backlight units, two or more gratingelements correspond to each pixel, and thus light beams transmitted byone pixel are simultaneously directed toward view points in severaldirections while having the same information, whereby the same image maybe simultaneously viewed in several directions and thus an angle forviewing a 3D image may be widened.

The provided directional backlight units may be mounted onautostereoscopic 3D display apparatuses (for example, TVs, monitors,tablets, and mobile devices).

The provided directional backlight units may widen a watching angle of a3D display apparatus.

The provided directional backlight units may easily apply an eyetracking method to 3D display apparatuses.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of exemplary embodiments,taken in conjunction with the accompanying drawings in which:

FIG. 1 is an exploded perspective view of a schematic opticalconstruction of a 3D image display apparatus, according to an exemplaryembodiment;

FIG. 2 schematically illustrates a positional relationship between adirectional backlight unit and a spatial light modulator of the 3D imagedisplay apparatus of FIG. 1;

FIG. 3 schematically illustrates views that are provided by the 3D imagedisplay apparatus of FIG. 1;

FIGS. 4A, 4B, 4C, and 4D schematically illustrate a difference betweenview points according to an exemplary embodiment and view pointsaccording to comparative examples;

FIG. 5 is an exploded perspective view of a schematic opticalconstruction of a 3D image display apparatus, according to an exemplaryembodiment;

FIG. 6 is an exploded perspective view of a 3D image display apparatus,according to another exemplary embodiment;

FIG. 7 is an exploded perspective view of a schematic opticalconstruction of a 3D image display apparatus, according to anotherexemplary embodiment;

FIG. 8 is an exploded perspective view of a schematic opticalconstruction of a 3D image display apparatus, according to anotherexemplary embodiment; and

FIG. 9 is an exploded perspective view of a 3D image display apparatus,according to another exemplary embodiment.

DETAILED DESCRIPTION

A directional backlight unit, a three-dimensional (3D) image displayapparatus, and a 3D image displaying method will now be described indetail with reference to the accompanying drawings. Like referencenumerals in the drawings denote like elements, and, in the drawings, thesizes of elements may be exaggerated for clarity and for convenience ofexplanation. It will be understood that when a material layer isreferred to as being “formed on” a substrate or another layer, it can bedirectly or indirectly formed on the substrate or the other layer. Thatis, for example, intervening layers may be present. Materials thatconstitute each layer in exemplary embodiments described below areexemplary, and thus the other materials may be used.

FIG. 1 is an exploded perspective view of a schematic opticalconstruction of a 3D image display apparatus 100, according to anexemplary embodiment. FIG. 2 schematically illustrates a positionalrelationship between a directional backlight unit 110 and a spatiallight modulator 150 of the 3D image display apparatus 100 of FIG. 1.FIG. 3 schematically illustrates first, second, and third groups of viewpoints V1, V2, . . . , V95, and V96; V1′, V2′, . . . , V95′, and V96′;and V1″, V2″, . . . , V95″, and V96″ that are provided by the 3D imagedisplay apparatus 100 of FIG. 1.

Referring to FIGS. 1 and 2, the 3D image display apparatus 100 accordingto the present exemplary embodiment includes the directional backlightunit (also referred to herein as a “directional backlight device”) 110,the spatial light modulator 150 including a plurality of pixels thatmodulate light beams emitted by the directional backlight unit 110, anda controller 190 that controls the directional backlight unit 110 andthe spatial light modulator 150.

The directional backlight unit 110 includes a light guide plate 111 anda light source unit (also referred to herein as a “light source device”)120 that is configured to provide light to the light guide plate 111. Aplurality of grating elements 112 that are configured to externally emitlight incident upon the light guide plate 111 are formed on an emissionsurface 111 a of the light guide plate 111.

The light source unit 120 may include a plurality of light sources 121disposed on an edge surface 111 b of the light guide plate 111. In otherwords, the directional backlight unit 110 according to the presentexemplary embodiment may adopt an edge type method. The light sources121 may be, for example, semiconductor light-emitting devices, such aslight-emitting diodes (LEDs). The light sources 121 may be monochromaticlight sources. In this case, the 3D image display apparatus 100 maydisplay a monochrome image (for example, a black-and-white image).Alternatively, the light sources 121 may include a red light source, agreen light source, and a blue light source. The red light source, thegreen light source, and the blue light source are driven in time series,and accordingly the spatial light modulator 150 may be driven to displaya color image.

The light guide plate 111 may be a flat panel formed of a transparentmaterial. In some cases, the light guide plate 111 may be a curved plateformed of a transparent material, or may be a flexible plate formed of atransparent material.

The plurality of grating elements 112 are two-dimensionally arranged onthe emission surface 111 a of the light guide plate 111. The emissionsurface 111 a may be a wide surface of the light guide plate 111 havinga flat panel shape (i.e., one of both flat panel surfaces). The gratingelements 112 may be respectively formed as, for example, a plurality ofpatterned grooves that are substantially parallel to the emissionsurface 111 a of the light guide plate 111. Light incident upon thelight guide plate 111 is totally reflected within the light guide plate111 and is then externally emitted via the grating elements 112. In thiscase, each of the grating elements 112 may be understood as a singleunit grating, and thus light is emitted while being diffracted. Thediffraction of light may depend on any one or more of a grating length,a grating width, a grating depth, a grating orientation, a gratingpitch, a duty cycle, and the like. As will be described below, theplurality of grating elements 112 may correspond to pixels 151 of thespatial light modulator 150 in a many-to-one correspondence, and thusthe grating elements 112 may be formed such that light beams emittedtherefrom are diffracted in different directions. A cross-sectionalshape of each of the grating elements 112 may be rectangular as shown inFIG. 2, but the exemplary embodiments are not limited thereto. Asanother example, a cross-section of each of the grating elements 112 mayhave a shape such as a triangle or a right triangle.

The spatial light modulator 150 includes a plurality of pixels 151arranged in a two-dimensional (2D) manner. Each of the pixels 151modulates light received via an electrical signal input. The modulationdenotes blocking or transmitting light or adjusting the amount of lighttransmitted. Each of the pixels 151 may be rectangular, but theexemplary embodiments are not limited thereto. For example, each of thepixels 151 may have a shape, such as a rectangle having rounded corners,a parallelogram, a diamond, or a circle.

The spatial light modulator 150 may be, for example, a transmissiveliquid crystal panel. The spatial light modulator 150 may have a flatpanel shape. As described above, when the light guide plate 111 has aflat panel shape, an interval between the light guide plate 111 and thespatial light modulator 150 may be constant. In some cases, since thelight guide plate 111 may be formed as a curved plate formed of atransparent material or as a flexible plate formed of a transparentmaterial, the interval between the light guide plate 111 and the spatiallight modulator 150 may not be constant. In addition, the spatial lightmodulator 150 may also be formed as a curved panel or a flexible panel.Thus, when both the light guide plate 111 and the spatial lightmodulator 150 are curved or flexible, the interval between the lightguide plate 111 and the spatial light modulator 150 may be constant.

The plurality of grating elements 112 may correspond to the pixels 151of the spatial light modulator 150 in a many-to-one correspondence, andthus the grating elements 112 may be grouped to form a plurality ofgroups. For example, the grating elements 112 may include a first groupof grating elements 112 a, a second group of grating elements 112 b, anda third group of grating elements 112 c. The grouping of the gratingelements 112 into three groups, which will now be described, is only anexample. According to another exemplary embodiment, the grating elements112 may be grouped into two groups or at least four groups.

The grating elements 112 a in the first group may correspond to thepixels 151 of the spatial light modulator 150 in a one-to-onecorrespondence, the grating elements 112 b in the second group maycorrespond to the pixels 151 of the spatial light modulator 150 in aone-to-one correspondence, and the grating elements 112 c in the thirdgroup may also correspond to the pixels 151 of the spatial lightmodulator 150 in a one-to-one correspondence. In other words, threegrating elements may match with each of the pixels 151 of the spatiallight modulator 150. The matching denotes that first light L1 emittedfrom one of the grating elements 112 a in the first group, second lightL2 emitted from one of the grating elements 112 b in the second group,and third light L3 emitted from one of the grating elements 112 c in thethird group pass through one of the pixels 151 and are directed towarddifferent view points. When the grating elements 112 are grouped intotwo groups or at least four groups according to another exemplaryembodiment as described above, two or at least four grating elements maymatch with each of the pixels 151 of the spatial light modulator 150.

In order for the grating elements 112 to emit light beams toward thepixels of the spatial light modulator 150 in a many-to-onecorrespondence and for light beams transmitted by the same pixel to bedirected toward different view points as described above, the gratingelements 112 may be formed to be different from each other in at leastone of a grating length, a grating width, a grating depth, a gratingorientation, a grating pitch, and a duty cycle. For example, the gratingelements 112 may have different grating orientations or differentgrating pitches so that light beams emitted from the grating elements112 may have different diffraction directions. When the grating elements112 are formed as grooves, a grating length may denote a groove length,a grating width may denote a groove width, a grating depth may denote agroove depth, a grating orientation may denote a width direction (or alength direction) of a groove, a grating pitch may denote an intervalbetween grooves, and a duty cycle may denote a ratio between the groovelength and the interval between grooves. Since the plurality of viewpoints may be arranged to be connected to one another in a horizontaldirection as will be described below, a grating element 112 a in thefirst group, a grating element 112 b in the second group, and a gratingelement 112 c in the third group corresponding to one pixel may bearranged in a horizontal direction. At least some of the gratingelements 112 may have different arrangement intervals. The arrangementinterval denotes a spatial interval between grating elements 112.Grating elements 112 corresponding to one pixel may have gratingelements 112 corresponding to another pixel therebetween. In some cases,the grating elements 112 corresponding to one pixel may be arrangedconsecutively.

An operation of the 3D image display apparatus 100 according to thepresent exemplary embodiment will presently be described.

The controller 190 controls the light source unit 120 to provide lightto the light guide plate 111.

As described above, since the first group of grating elements 112 a isformed on the emission surface 111 a of the light guide plate 111, thegrating elements 112 a in the first group on the light guide plate 111emit first light beams L1 toward corresponding pixels 151 of the spatiallight modulator 150. The first light beams L1 transmitted by the pixels151 of the spatial light modulator 150 form a first group of view pointsV1, V2, . . . , V95, and V96 (see FIG. 3). Although 96 view points V1,V2, . . . , V95, and V96 are formed the first group in FIG. 3, this isonly an example, and less or more view points than the 96 view pointsmay be formed.

The grating elements 112 b in the second group on the light guide plate111 emit second light beams L2, and the second light beams L2 propagatethrough corresponding pixels 151 of the spatial light modulator 150 andthen form a second group of view points V1′, V2′, . . . , V95′, and V96′(see FIG. 3). The grating elements 112 c in the third group on the lightguide plate 111 emit third light beams L3, and the third light beams L3propagate through corresponding pixels 151 of the spatial lightmodulator 150 and then form a third group of view points V1″, V2″, . . ., V95″, and V96″ (see FIG. 3). At this time, a first region R1, in whichthe first group of view points V1, V2, . . . , V95, and V96 are formed,a second region R2, in which the second group of view points V1′, V2′, .. . , V95′, and V96′ are formed, and a third region R3, in which thethird group of view points V1″, V2″, . . . , V95″, and V96″ are formed,do not overlap with one another. As shown in FIG. 3, the second group ofview points V1′, V2′, . . . , V95′, and V96′ may be arranged after thefirst group of view points V1, V2, . . . , V95, and V96, and the thirdgroup of view points V1″, V2″, . . . , V95″, and V96″ may be arrangedafter the second group of view points V1′, V2′, . . . , V95′, and V96′.

As shown in FIG. 3, the first, second, and third groups of view pointsV1, V2, . . . , V95, and V96; V1′, V2′, . . . , V95′, and V96′; and V1″,V2″, . . . , V95″, and V96″ may be consecutively arranged in acircumferential direction at intervals of a distance that is less thanor equal to an average binocular distance of a viewer (e.g., 6.1 cm), ata predetermined watching distance. For example, intervals between thefirst group of view points V1, V2, . . . , V95, and V96 may each beapproximately equal to a pupil size of the viewer.

The controller 190 controls the spatial light modulator 150 to modulatethe first, second, and third light beams L1, L2, and L3, therebyenabling an image to be viewed at the first, second, and third groups ofview points V1, V2, . . . , V95, and V96; V1′, V2′, . . . , V95′, andV96′; and V1″, V2″, . . . , V95″, and V96″. Images that are viewed ateach of the first, second, and third groups of view points V1, V2, . . ., V95, and V96; V1′, V2′, . . . , V95′, and V96′; and V1″, V2″, . . . ,V95″, and V96″ are two-dimensional (2D) images. For example, when thedirectional backlight unit 110 forms 96 view points for each group, asshown in FIG. 3, a 2D image viewed at one view point corresponding toone eye of the viewer (e.g., the view point V1) may be generated by 1/96of the pixels 151. The number of pixels contributing to 2D imagegeneration for each view point is exemplary, and may vary based on imagegenerating methods. When the spatial light modulator 150 displays a 3Dimage, the 2D images viewed at the first group of view points V1, V2, .. . , V95, and V96 are formed to have a binocular parallax between viewpoints spaced apart at an interval corresponding to the binoculardistance of the viewer, thereby enabling the viewer to experience astereoscopic effect via both eyes. For example, in FIG. 3, a view pointVm′ and a view point Vn′ are spaced apart from each other by an averagebinocular distance of the viewer, and an image viewed at the view pointVm′ and an image viewed at the view point Vn′ may have a binocularparallax. When the spatial light modulator 150 displays a 2D image, thespatial light modulator 150 modulates the first light beams L1 so thatthese 2D images are the same images and thus do not have a binocularparallax. Since images formed at the second group of view points V1′,V2′, . . . , V95′, and V96′ or the third group of view points V1″, V2′,. . . , V95″, and V96″ have passed through pixels 151 of the spatiallight modulator 150 that form images of the first group of view pointsV1, V2, . . . , V95, and V96, the images formed at the second group ofview points V1′, V2′, . . . , V95′, and V96′ or the third group of viewpoints V1″, V2′, . . . , V95″, and V96″ are the same as the images ofthe first group of view points V1, V2, . . . , V95, and V96. In otherwords, the 3D images of a binocular parallax shown at the first group ofview points V1, V2, . . . , V95, and V96 may be repeatedly shown at thesecond group of view points V1′, V2′, . . . , V95′, and V96′ or thethird group of view points V1″, V2″, . . . , V95″, and V96″.

FIGS. 4A, 4B, 4C, and 4D schematically illustrate a difference betweenview points according to an exemplary embodiment and view pointsaccording to comparative examples. Table 1 below shows thecharacteristics of 3D images according to the present exemplaryembodiment and the comparative examples.

TABLE 1 Interval Watch- between ing Number view points 3D Stereo- degreeof view (@ 0.5 m resolu- scopic (deg) points (mm) tion effectComparative 40° 96 6.1 Example 1 Comparative 80° 96 12.2 DegradedExample 2 Comparative 80° 192 6.1 Degraded Example 3 Exemplary 80° 966.1 Embodiment 1

FIG. 4A illustrates a case in which a 3D display apparatus forms 96 viewpoints, and the case of FIG. 4A corresponds to Comparative Example 1 inTable 1. The 96 view points are arranged at intervals of 6.1 mm at awatching distance of 0.5 m. In this case, a watching angle (i.e., aviewing angle at which a viewer views a 3D image) is restricted to aregion that forms the 96 view points, for example, to 40°.

FIG. 4B illustrates a case in which a 3D display apparatus forms 96 viewpoints and widens an interval between the 96 view points to 12.2 mm atthe viewing distance of 0.5 m in order to increase the watching angle atwhich a viewer is able to view a 3D image. The case of FIG. 4Bcorresponds to Comparative Example 2 in Table 1. In this case, as theinterval between the 96 view points is doubled, when the viewer moves,the degree of a variation of an image becomes relatively slow accordingto a time difference corresponding to the movement amount, and thus a 3Deffect is degraded.

FIG. 4C illustrates a case in which a 3D display apparatus forms 192view points, and the case of FIG. 4C corresponds to Comparative Example3 in Table 1. In this case, an interval between the 192 view pointsmaintains the interval between the 96 view points in FIG. 4A, but theresolution of an image viewed at each view point is halved. Theresolution of an image viewed at each view point in the comparativeexamples is a result of splitting the overall resolution of a spatiallight modulator by the number of view points. However, when the numberof view points is increased as in Comparative Example 3, a resolution ateach view point is decreased, and consequently a 3D resolution isdegraded.

FIG. 4D illustrates a case in which a 3D display apparatus repeats the96 view points to form two groups, and the case of FIG. 4D correspondsto Exemplary Embodiment 1 in Table 1. Exemplary Embodiment 1 is a casein which two groups of grating elements are provided on a light guideplate of a directional backlight unit such that two grating elementsmatch with each pixel of a spatial light modulator and in which thegrating elements in each of the two groups form 96 view points. In thiscase, an inter-view interval maintains the interval between the viewpoints in FIG. 4A, and the overall number of view points is 192 and thusa wide watching angle is secured. Moreover, since two groups of viewpoints are repeated, the resolution of an image viewed at each viewpoint is a result of splitting the overall resolution of the spatiallight modulator by the number of view points included in each group.Thus, a phenomenon in which a 3D resolution is degraded instead ofincreasing a watching angle as in Comparative Example 3 does not occur,and a 3D effect is not degraded since the inter-view interval is notincreased.

Although a case in which the first, second, and third groups of viewpoints V1, V2, . . . , V95, and V96; V1′, V2′, . . . , V95′, and V96′;and V1″, V2″, . . . , V95″, and V96″ are repeated and arranged in acircumferential direction is illustrated in the above-describedexemplary embodiments, the exemplary embodiments are not limitedthereto. For example, the first, second, and third groups of gratingelements 112 a, 112 b, and 112 c may be formed such that the secondgroup of view points V1′, V2′, . . . , V95′, and V96′ or the third groupof view points V1″, V2″, . . . , V95″, and V96″ may be positioned in avertical direction of the first group of view points V1, V2, . . . ,V95, and V96.

FIG. 5 is an exploded perspective view of a schematic opticalconstruction of a 3D image display apparatus 200, according to anotherexemplary embodiment.

Referring to FIG. 5, the 3D image display apparatus 200 according to thepresent exemplary embodiment includes a directional backlight unit (alsoreferred to herein as a “directional backlight device”) 210, a spatiallight modulator 250, a color filter 260, and a controller 290 that isconfigured to control the directional backlight unit 210 and the spatiallight modulator 250. The 3D image display apparatus 200 according to thepresent exemplary embodiment is substantially the same as the 3D imagedisplay apparatus 100 according to the previous exemplary embodimentexcept that the color filter 260 is further included, and thus thisdifference will be described in detail below.

The directional backlight unit 210 includes a light guide plate 211 anda light source unit (also referred to herein as a “light source device”)220 that is configured to provide light to the light guide plate 211. Aplurality of grating elements 212 externally emitting light incidentupon the light guide plate 211 are formed on an emission surface 211 aof the light guide plate 211. The light source unit 220 may include aplurality of red, green, and blue light sources 221 disposed on an edgesurface 211 b of the light guide plate 211.

The spatial light modulator 250 includes a plurality of sub-pixels 251arranged in a 2D manner. The sub-pixels 251 may include red sub-pixels251R, green sub-pixels 251G, and blue sub-pixels 251B. A red sub-pixel251R, a green sub-pixel 251G, and a blue sub-pixel 251B are arrangedside by side in a width direction thereof and thus form a pixel. Each ofthe sub-pixels 251 may have a rectangular shape that is longer in onedirection. The color filter 260 may include pixel filters 261 includingred pixel filters 261R, green pixel filters 261G, and blue pixel filters261B such that the pixel filters correspond to the red sub-pixels 251R,the green sub-pixels 251G, and the blue sub-pixels 251B in a one-to-onecorrespondence. The red, green, and blue sub-pixels 251R, 251G, and 251Bmay modulate light, and the red, green, and blue pixel filters 261R,261G, and 261B may transmit red, green, and blue light beams,respectively, and may block light from sub-pixels of different colorsfrom the sub-pixels corresponding to the red, green, and blue pixelfilters 261R, 261G, and 261B due to dispersion of light, to therebyreduce the number of unwanted signals. In FIG. 5, the spatial lightmodulator 250 and the color filter 260 are spaced apart from each other.However, this is for convenience of explanation, and the spatial lightmodulator 250 and the color filter 260 may be disposed close to eachother to form a single display panel. A case where the sub-pixels 251form a single pixel by using red, green, and blue sub-pixels and each ofthe sub-pixels 251 has a rectangular shape will now be described, butthe exemplary embodiments are not limited thereto. According to anotherexemplary embodiment, the color combination of the sub-pixels 251 toform a single pixel may be varied, and the shape of each of thesub-pixels 251 or the arrangement of the sub-pixels 251 may be varied.For example, each of the sub-pixels 251 may have a shape, such as arectangle having rounded corners, a parallelogram, a diamond, or acircle, and the sub-pixels 251 may have a slightly-inclined arrangementor a zigzag arrangement.

The plurality of grating elements 212 may correspond to the sub-pixels251 of the spatial light modulator 250 in a many-to-one correspondence,and thus the grating elements 212 may be grouped to form a plurality ofgroups. For example, the grating elements 212 may be grouped into, forexample, three groups. In other words, the grating elements 212 mayinclude a first group of grating elements 212 a, a second group ofgrating elements 212 b, and a third group of grating elements 212 c. Thegrating elements 212 a in the first group may correspond to thesub-pixels 251 of the spatial light modulator 250 in a one-to-onecorrespondence, the grating elements 212 b in the second group maycorrespond to the sub-pixels 251 of the spatial light modulator 250 in aone-to-one correspondence, and the grating elements 212 c in the thirdgroup may also correspond to the sub-pixels 251 of the spatial lightmodulator 250 in a one-to-one correspondence. Since each of thesub-pixels 251 may have a rectangular shape that is longer in onedirection as described above, three rows of the first, second, and thirdgroups of grating elements 212 a, 212 b, and 212 c may correspond to onerow of sub-pixels 251 in the width direction of the sub-pixels 251. Inother words, grating elements 212 corresponding to one sub-pixel 251 maybe understood as three parts into which the sub-pixel 251 is split in alength direction thereof (in the vertical direction in FIG. 5). Based onthe length direction of the sub-pixels 251, the overall number of rowsof the grating elements 212 may be equal to an integer multiple of thenumber of rows of the sub-pixels 251. Grating shapes or arrangementintervals of the grating elements 212 may be different from one anotherso that light beams are emitted from the grating elements 212, propagatethrough corresponding sub-pixels 251, and then form different viewpoints.

The grouping of the grating elements 212 into three groups in the abovedescription is only an example. According to another exemplaryembodiment, the grating elements 212 may be grouped into two groups orat least four groups.

In the above-described exemplary embodiments, the 3D image displayapparatuses 100 and 200 include the edge-type directional backlightunits 110 and 210, respectively, that is, the light source units 120 and220 are positioned on respective edge surfaces of the light guide plates111 and 211. However, the exemplary embodiments are not limited thereto.

FIG. 6 is an exploded perspective view of a 3D image display apparatus300 according to another exemplary embodiment. Referring to FIG. 6, the3D image display apparatus 300 according to the present exemplaryembodiment includes a directional backlight unit 310, a spatial lightmodulator 350, a color filter 360, and a controller 390 that isconfigured to control the directional backlight unit 310 and the spatiallight modulator 350. The directional backlight unit 310 includes aplurality of grating elements 312 on a front surface 311 a of a lightguide plate 311, and a light source unit 320 is disposed on a rearsurface 311 b of the light guide plate 311. For example, the lightsource unit 320 may include a plurality of light sources 321 arranged ina 2D manner. The light sources 321 may be red, green, and blue lightsources. As another example, the light sources 321 of the light sourceunit 320 maybe white light sources, and a color may be realized via thecolor filter 360. The plurality of grating elements 312, arranged on thefront surface 311 a of the light guide plate 311, the spatial lightmodulator 350, and the color filter 360 are substantially the same asthose in the previously described exemplary embodiments, and thusdetailed descriptions thereof will be omitted here.

In the above-described exemplary embodiments, the 3D image displayapparatuses 100, 200, and 300 include the directional backlight units110, 210, and 310 respectively including the single light guide plate111, the single light guide plate 211, and single light guide plate 311.However, the exemplary embodiments are not limited thereto.

FIG. 7 is an exploded perspective view of a 3D image display apparatus400 according to another exemplary embodiment. Referring to FIG. 7, the3D image display apparatus 400 according to the present exemplaryembodiment includes a directional backlight unit 410, a spatial lightmodulator 450, and a controller (not shown) configured to control thedirectional backlight unit 410 and the spatial light modulator 450.

The directional backlight unit 410 may include first, second, and thirdbacklight units 410 a, 410 b, and 410 c which are optically separatedfrom one another. The first, second, and third backlight units 410 a,410 b, and 410 c may include first, second, and third light guide plates411 a, 411 b, and 411 c, respectively. The first, second, and thirdlight guide plates 411 a, 411 b, and 411 c may be stacked one onanother. In detail, the first light guide plate 411 a may be staked overan upper surface of the second light guide plate 411 b, and the secondlight guide plate 411 b may be stacked over an upper surface of thethird light guide plate 411 c. The upper surfaces of the second andthird light guide plates 411 b and 411 c may denote emission surfaces ofthe second and third light guide plates 411 b and 411 c. The first,second, and third light guide plates 411 a, 411 b, and 411 c may bestacked one on another without having spaces therebetween or may bestacked one on another with spaces therebetween. The first, second, andthird light guide plates 411 a, 411 b, and 411 c may be stacked one onanother slightly in a zigzag manner. A light source unit (not shown) maybe disposed on edge surfaces of the first, second, and third light guideplates 411 a, 411 b, and 411 c.

First, second, and third grating elements 412 a, 412 b, and 412 c may beprovided on the respective emission surfaces of the first, second, andthird light guide plates 411 a, 411 b, and 411 c, respectively. Thefirst, second, and third grating elements 412 a, 412 b, and 412 c maycorrespond to pixels 451 of the spatial light modulator 450 in amany-to-one correspondence, and accordingly, the first, second, andthird grating elements 412 a, 412 b, and 412 c may be grouped into, forexample, first, second, and third groups. The grating elements 412 a inthe first group may correspond to the pixels 451 of the spatial lightmodulator 450 in a one-to-one correspondence, the grating elements 412 bin the second group may correspond to the pixels 451 of the spatiallight modulator 450 in a one-to-one correspondence, and the gratingelements 412 c in the third group may also correspond to the pixels 450of the spatial light modulator 450 in a one-to-one correspondence. Indetail, first light L1 emitted from one of the grating elements 412 a inthe first group directly passes through one of the pixels 451. Secondlight L2 emitted from one of the grating elements 412 b in the secondgroup passes through one of the pixels 451 via the first light guideplate 411 a. At this time, the second light L2 may pass through firstgrating elements 412 a provided on the first light guide plate 411 a ormay be blocked thereby. Even if the second light L2 passes through thefirst grating elements 412 a provided on the first light guide plate 411a, an optical intensity of high-level diffracted light becomes veryweak, and thus an image viewed by a viewer may not be greatly degraded.Third light L3 emitted from one of the grating elements 412 c in thethird group passes through one of the pixels 451 via the second lightguide plate 411 b and the first light guide plate 411 a. At this time,the third light L3 may pass through second grating elements 412 bprovided on the second light guide plate 411 b or first grating elements412 a provided on the first light guide plate 411 a or may be blockedthereby. The first, second, and third lights L1, L2, and L3 respectivelyemitted by the first, second, and third grating elements 412 a, 412 b,and 412 c pass through the same pixel and then are directed towarddifferent view points.

According to the present exemplary embodiment, the first, second, andthird backlight units 410 a, 410 b, and 410 c may be independentlydriven. Since the first backlight unit 410 a emit first lights L1heading for a first group of view points, if a viewer exists within aregion of the first group of view points, only the first backlight unit410 a may be driven. A 3D image display apparatus employing an eyetracking device as in an exemplary embodiment, which will be describedbelow, may detect a user's eyes and drive only a backlight unitincluding views that correspond to the detected user's eyes.

Although the first, second, and third grating elements 412 a, 412 b, and412 c are provided on the respective emission surfaces of the first,second, and third light guide plates 411 a, 411 b, and 411 c in thepresent exemplary embodiment, the exemplary embodiments are not limitedthereto. For example, the first grating elements 412 a may be scatteredand provided on the respective emission surfaces of the first, second,and third light guide plates 411 a, 411 b, and 411 c, and the second andthird grating elements 412 b and 412 c may also be scattered andprovided on the respective emission surfaces of the first, second, andthird light guide plates 411 a, 411 b, and 411 c.

Although the directional backlight unit 410 is a stack of three lightguide plates in the present exemplary embodiment, the directionalbacklight unit 410 may be a stack of two or at least four light guideplates.

FIG. 8 is an exploded perspective view of a 3D image display apparatus500 according to another exemplary embodiment. Referring to FIG. 8, the3D image display apparatus 500 according to the present exemplaryembodiment includes a directional backlight unit 510, a spatial lightmodulator 550, and a controller (not shown) configured to control thedirectional backlight unit 510 and the spatial light modulator 550.

The directional backlight unit 510 may include first, second, and thirdbacklight units 510 a, 510 b, and 510 c. The first, second, and thirdbacklight units 510 a, 510 b, and 510 c may include first, second, andthird light guide plates 511 a, 511 b, and 511 c, respectively. Thefirst, second, and third light guide plates 511 a, 511 b, and 511 c maybe arranged side by side in a horizontal direction. In detail, thesecond light guide plate 511 b may be disposed to be separated from arear surface of the spatial light modulator 550, the first light guideplate 511 a may be disposed on the left side of the second light guideplate 511 b to be slightly inclined with respect to the spatial lightmodulator 550, and the third light guide plate 511 c may be disposed onthe right side of the second light guide plate 511 b to be slightlyinclined with respect to the spatial light modulator 550. A light sourceunit (not shown) may be disposed on edge surfaces or rear surfaces ofthe first, second, and third light guide plates 511 a, 511 b, and 511 c.

First, second, and third grating elements 512 a, 512 b, and 512 c may beprovided on the respective emission surfaces of the first through thirdlight guide plates 511 a, 511 b, and 511 c, respectively. The first,second, and third grating elements 512 a, 512 b, and 512 c maycorrespond to pixels 551 of the spatial light modulator 550 in athree-to-one correspondence and thus may be grouped into three groups.The grating elements 512 a in the first group may correspond to thepixels 551 of the spatial light modulator 550 in a one-to-onecorrespondence, the grating elements 512 b in the second group maycorrespond to the pixels 551 of the spatial light modulator 550 in aone-to-one correspondence, and the grating elements 512 c in the thirdgroup may also correspond to the pixels 551 of the spatial lightmodulator 550 in a one-to-one correspondence. The respective numbers offirst, second, and third grating elements 512 a, 512 b, and 512 cprovided on the first, second, and third light guide plates 511 a, 511b, and 511 c may be substantially the same as the number of pixels 551of the spatial light modulator 550. Although the first, second, andthird grating elements 512 a, 512 b, and 512 c are provided on therespective emission surfaces of the first, second, and third light guideplates 511 a, 511 b, and 511 c in the present exemplary embodiment, theexemplary embodiments are not limited thereto. For example, the firstgrating elements 512 a may be scattered and provided on the respectiveemission surfaces of the first, second, and third light guide plates 511a, 511 b, and 511 c, and the second and third grating elements 512 b and512 c may also be scattered and provided on the respective emissionsurfaces of the first, second, and third light guide plates 511 a, 511b, and 511 c. The respective numbers of first, second, and third gratingelements 512 a, 512 b, and 512 c respectively provided on the first,second, and third light guide plates 511 a, 511 b, and 511 c may bedifferent from one another.

Although the directional backlight unit 510 is a side-by-sidearrangement of three light guide plates in the present exemplaryembodiment, the directional backlight unit 510 may be a side-by-sidearrangement of two or at least four light guide plates. The directionalbacklight unit 510 may also be a stack of light guide plates as in theembodiment of FIG. 7, instead of a side-by-side arrangement of lightguide plates.

Although the first and third light guide plate 511 a and 511 c areslightly inclined with respect to the second light guide plate 511 b inthe present exemplary embodiment, the exemplary embodiments are notlimited thereto. For example, the first, second, and third light guideplates 511 a, 511 b, and 511 c may be disposed on a plane. As anotherexample, the first, second, and third light guide plates 511 a, 511 b,and 511 c may be disposed on a curved surface.

Although the first and third light guide plate 511 a and 511 c arejuxtaposed in a horizontal direction in the present exemplaryembodiment, the exemplary embodiments are not limited thereto. Forexample, the first and third light guide plates 511 a and 511 c may berespectively disposed over and below the second light guide plate 511 b.

FIG. 9 is an exploded perspective view of a 3D image display apparatus600, according to another exemplary embodiment. Referring to FIG. 9, the3D image display apparatus 600 according to the present exemplaryembodiment includes a display unit (also referred to herein as a“display device” and/or as a “display”) 610, an eye tracking device 620,and a controller 630 configured to control the display unit 610 and theeye tracking device 620.

The display unit 610 may be any of the 3D image display apparatusesaccording to the previously described exemplary embodiments. The eyetracking device 620 tracks a left eye E_(L) and/or a right eye E_(R) ofa viewer 601. The eye tracking device 620 may include a camera, andextract and track the left eye E_(L) and/or the right eye E_(R) from aface image of the viewer 601 captured by the camera. A process ofextracting the left eye E_(L) and/or the right eye E_(R) from the faceimage of the viewer 601 may be independently performed within the eyetracking device 620 or may be performed within the controller 630.

In an operation of the 3D image display apparatus 600 according to thepresent exemplary embodiment, for convenience of explanation, thedisplay unit 610 forms six view points V1, V2, V3, V4, V5, and V6 for afirst group, six view points V1′, V2′, V3′, V4′, V5′, and V6′ for asecond group, and six view points V1″, V2″, V3″, V4″, V5″, and V6″ for athird group, and an inter-view interval is a binocular parallaxinterval. The first group of view points V1, V2, V3, V4, V5, and V6, thesecond group of view points V1′, V2′, V3′, V4′, V5′, and V6′, and thethird group of view points V1″, V2″, V3″, V4″, V5″, and V6″ repeat thesame image. The view points in each group have a binocular parallax.When the viewer 601 view points an image within the first group of viewpoints V1, V2, V3, V4, V5, and V6, the second group of view points V1′,V2′, V3′, V4′, V5′, and V6′, or the third group of view points V1″, V2″,V3″, V4″, V5″, and V6″, the viewer 601 views a 3D stereoscopic image dueto a binocular parallax. If the left eye E_(L) of the viewer 601 is atthe view point V3′ and the right eye E_(R) of the viewer 601 is at theview point V4′ as shown in FIG. 9, the viewer 601 feels a stereoscopiceffect due to a binocular parallax between an image shown at the viewpoint V3′ and an image shown at the view point V4′. However, when theviewer 601 moves to a side 602, the left eye E_(L) of the viewer 601 maybe at the view point V6′ and the right eye E_(R) of the viewer 601 is atthe view point V1″. However, according to the above-described exemplaryembodiments, since an image shown at the view point V1″ is substantiallythe same as an image shown at the view point V1′, an image shown at theview point V6′ and the image shown at the view point V1″ may be mirrorimages. Accordingly, in the present exemplary embodiment, when the eyetracking device 620 detects that the left eye E_(L) and the right eyeE_(R) of the viewer 601 are at a boundary between view points (forexample, between the view points V6 and V1′ and the view points V6′ andV1″) or the viewer 601 moves toward the boundary between the viewpoints, the 3D image display apparatus 600 appropriately moves an imagedisplayed on the display unit 610 in order to display an image having aproper binocular parallax before a viewer views a mirror image. Forexample, when the viewer 601 moves to the side 602 and thus the left eyeE_(L) of the viewer 601 is at the view point V6′ and the right eye E_(R)of the viewer 601 is at the view point V1″, an image previouslydisplayed at the first group of view points V1, V2, V3, V4, V5, and V6,the second group of view points V1′, V2′, V3′, V4′, V5′, and V6′, andthe third group of view points V1″, V2″, V3″, V4″, V5″, and V6″ is movedto the side 602 so that the viewer 601 views an image having a properbinocular parallax.

Although a directional backlight unit, a 3D image display apparatus, anda 3D image displaying method according to one or more exemplaryembodiments have been described with reference to the exemplaryembodiments illustrated in the drawings in order to facilitateunderstanding of the present inventive concept, the illustratedembodiments are only examples, and various modifications to theillustrated embodiments and other equivalent embodiments may bepossible. Therefore, the scope of the present inventive concept shouldbe determined by the accompanying claims.

It should be understood that exemplary embodiments described hereinshould be considered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each exemplaryembodiment should typically be considered as available for other similarfeatures or aspects in other embodiments.

While the present inventive concept has been particularly shown anddescribed with reference to exemplary embodiments thereof, it will beunderstood by those of ordinary skill in the art that various changes inform and details may be made therein without departing from the spiritand scope of the present inventive concept as defined by the followingclaims.

What is claimed is:
 1. A directional backlight device comprising: atleast one light guide plate; a light source configured to provide lightto the at least one light guide plate; and a first group of gratingelements and a second group of grating elements disposed on an emissionsurface of the at least one light guide plate and configured toexternally emit the light from the emission surface, wherein each of thefirst group of grating elements and the second group of grating elementsis arranged such that light beams emitted by the first group of gratingelements propagate through a plurality of pixel points spaced apart fromthe emission surface and form a first group of view points, that lightbeams emitted from the second group of grating elements propagatethrough the plurality of pixel points and form a second group of viewpoints, and that a region within which the second group of view pointsis formed does not overlap with a region within which the first group ofview points is formed.
 2. The directional backlight device of claim 1,wherein the view points in the first group are consecutively arranged,and the view points in second group are consecutively arranged after thefirst group of view points.
 3. The directional backlight device of claim1, wherein at least two light beams propagate through each of theplurality of pixel points, and the at least two light beams comprise afirst light beam emitted from one of the grating elements included inthe first group and a second light beam emitted from one of the gratingelements included in the second group.
 4. The directional backlightdevice of claim 1, wherein light beams emitted from two adjacent gratingelements among the first and second groups of grating elements aredirected to different pixel points.
 5. The directional backlight deviceof claim 1, wherein each of the first group of grating elements and thesecond group of grating elements includes a respective plurality ofpatterned grooves that are substantially parallel to one another.
 6. Thedirectional backlight device of claim 5, wherein the first and secondgroups of grating elements are different from each other with respect toat least one from among a grating length, a grating width, a gratingdepth, a grating orientation, a grating pitch, and a duty cycle.
 7. Thedirectional backlight device of claim 1, wherein at least two gratingelements from within the first and second groups of grating elements aredifferent from each other with respect to an arrangement interval. 8.The directional backlight device of claim 1, wherein intervals betweenadjacent pairs of grating elements in each of the first and secondgroups of grating elements and adjacent pairs of pixel points in theplurality of pixel points are substantially constant.
 9. The directionalbacklight device of claim 1, wherein a number of grating elementsincluded in the first group is equal to a number of pixel pointsincluded in the plurality of pixel points.
 10. The directional backlightdevice of claim 1, wherein a number of grating elements included in thefirst group is equal to a number of grating elements included in thesecond group.
 11. The directional backlight device of claim 1, whereinthe at least one light guide plate comprises a single light guide plate.12. The directional backlight device of claim 1, wherein the at leastone light guide plate comprises a first light guide plate and a secondlight guide plate that are optically separated from each other, and atleast two of the grating elements included in the first and secondgroups are disposed on the first light guide plate, and all othergrating elements included in the first and second groups are disposed onthe second light guide plate.
 13. The directional backlight device ofclaim 12, wherein a number of grating elements disposed on each of thefirst and second light guide plates is equal to a number of pixel pointsincluded in the plurality of pixel points.
 14. The directional backlightdevice of claim 12, wherein the first group of grating elements isdisposed on the first light guide plate and the second group of gratingelements is disposed on the second light guide plate.
 15. Thedirectional backlight device of claim 12, wherein the first and secondlight guide plates are disposed side by side in a lateral direction. 16.The directional backlight device of claim 15, wherein the second lightguide plate is inclined with respect to the first light guide plate. 17.The directional backlight device of claim 12, wherein the first lightguide plate is stacked on the second light guide plate.
 18. Adirectional backlight device comprising: a light guide plate; a lightsource configured to provide light to the light guide plate; and aplurality of grating elements provided on an emission surface of thelight guide plate and configured to externally emit the light from theemission surface such that the light propagates through a plurality ofpixel points spaced apart from the emission surface, wherein at leasttwo of the plurality of grating elements match with each pixel pointfrom among the plurality of pixel points, two adjacent grating elementsmatch with different pixel points from among the plurality of pixelpoints, and light beams emitted from the at least two grating elementspropagate through one pixel point matched with the at least two gratingelements and then are directed toward different view points.
 19. Thedirectional backlight device of claim 18, wherein an overall number ofgrating elements is an integer multiple of a number of pixel pointsincluded in the plurality of pixel points.
 20. The directional backlightunit of claim 18, wherein the plurality of grating elements are arrangedsuch that light beams emitted from the plurality of grating elementspropagate through the plurality of pixel points and form a plurality ofgroups of view points and that regions within which different groups ofview points are formed do not overlap with each other.
 21. Athree-dimensional (3D) image display apparatus comprising: a directionalbacklight device comprising a light guide plate, a light sourceconfigured to provide light to the light guide plate, and first andsecond groups of grating elements disposed on an emission surface of thelight guide plate and configured to externally emit the light from theemission surface; a spatial light modulator comprising a plurality ofpixels that modulate light beams emitted by the directional backlightdevice; and a controller configured to control the directional backlightdevice and the spatial light modulator, wherein the first and secondgroups of grating elements are arranged such that light beams emittedfrom the first group of grating elements propagate through the pluralityof pixels of the spatial light modulator and form a first group of viewpoints, that light beams emitted from the second group of gratingelements propagate through the plurality of pixels of the spatial lightmodulator and form a second group of view points, and that a regionwithin which the second group of view points is formed does not overlapwith a region within which the first group of view points is formed. 22.The 3D image display apparatus of claim 21, wherein the view points inthe first group are consecutively arranged, and the view points insecond group are consecutively arranged after the first group of viewpoints.
 23. The 3D image display apparatus of claim 21, wherein at leasttwo light beams propagate through each of the plurality of pixel points,and the at least two light beams comprise a first light beam emittedfrom one of the grating elements included in the first group and asecond light beam emitted from one of the grating elements included inthe second group.
 24. The 3D image display apparatus of claim 21,wherein 3D images shown at the first group of view points are repeatedlyshown at the second group of view points.
 25. The 3D image displayapparatus of claim 21, wherein the spatial light modulator comprises aplurality of sub-pixels for each pixel included in the plurality ofpixels, and each of the sub-pixels of the spatial light modulatortransmits light beams emitted from at least two grating elements. 26.The 3D image display apparatus of claim 25, wherein each of thesub-pixels has a rectangular shape that is longer in a lengthwisedirection and adjacent pairs of sub-pixels from among the plurality ofsub-pixels in each pixel are arranged side by side in a widthwisedirection thereof, and in the lengthwise direction of the sub-pixels, anoverall number of rows of the first and second groups of gratingelements is an integer multiple of a number of rows of the sub-pixels.27. The 3D image display apparatus of claim 21, further comprising aneye tracking device configured to track eyes of a viewer, wherein thecontroller is further configured to control the spatial light modulatorso that pixels corresponding to the eyes of the viewer tracked by theeye tracking device generate an image.
 28. A 3D image displaying methodcomprising: providing light to a light guide plate; arranging aplurality of grating elements comprising first and second groups ofgrating elements on an emission surface of the light guide plate suchthat the grating elements are configured to externally emit the lightfrom the emission surface; modulating emitted light beams by using aplurality of pixels of a spatial light modulator; and forming a firstgroup of view points by facilitating a propagation of light beamsemitted from the first group of grating elements through the pluralityof pixels of the spatial light modulator, and forming a second group ofview points by facilitating a propagation of light beams emitted fromthe second group of grating elements through the plurality of pixels ofthe spatial light modulator, wherein a region within which the secondgroup of view points is formed does not overlap with a region withinwhich the first group of view points is formed.
 29. The 3D imagedisplaying method of claim 28, wherein the view points in the firstgroup are consecutively arranged, and the view points in the secondgroup are consecutively arranged after the first group of view points.30. The 3D image displaying method of claim 28, wherein at least twolight beams propagate through each of the plurality of pixel points, andthe at least two light beams comprise a first light beam emitted fromone of the grating elements included in the first group and a secondlight beam emitted from one of the grating elements included in thesecond group.
 31. The 3D image displaying method of claim 28, whereinlight beams emitted from two adjacent grating elements from among thefirst and second groups of grating elements are directed to differentpixels.
 32. The 3D image displaying method of claim 28, wherein 3Dimages shown at the first group of view points are repeatedly shown atthe second group of view points.
 33. The 3D image displaying method ofclaim 28, further comprising tracking eyes of a viewer, wherein thespatial light modulator is controlled so that pixels corresponding tothe tracked eyes of the viewer generate an image.